All true, no quarrel. But I think you'll find the 'show SGA' command to be
as misleading on Solaris as it is on Windows, and Linux for that matter:
that is, it will still report SGA_MAX being used, even when it isn't.
Regards
HJR
"Thomas Kyte" <tkyte_at_oracle.com> wrote in message
news:af4ove02c6c_at_drn.newsguy.com...
> In article <3D15BE67.1060506_at_europe.com>, sg says...
> >
> >does this apply to all platforms?
> >
>
> no, see
>
http://technet.oracle.com/docs/products/oracle9i/doc_library/901_doc/A90347-
02/html/ch1_admi.htm#86752
>
> for example where it discusses ISM vs DISM on solaris.
>
> But -- bear in mind, that one a platform like windows where it must do
this (in
> order to keep the memory space "flat" -- we cannot just realloc() the
memory, it
> would move the entire SGA -- leaving a really big, huge hole in the
processes
> already allocated memory), the OS will do the right thing. That is -- if
we ask
> for 500m, but use only 200m -- the other 300m will be paged out, the OS
won't
> reserve physical ram for us. If you never grow the SGA, that memory will
never
> be paged in.
>
>
>
>
> >cheers
> >
> >Howard J. Rogers wrote:
> >
> >> Yup.
> >>
> >> Set SGA_MAX_SIZE to X, and Oracle nabs the whole of X from the O/S,
even if
> >> then doesn't go on to allocate all of X to the various components of
the
> >> SGA. The 'show SGA' command then displays what has been reserved, not
what
> >> is actually in use (which is a shame, I think, but you leanr to live
with
> >> these things).
> >>
> >> It has to be this way (the reserving, not the displaying), because when
you
> >> dynamically increase the buffer cache or shared_pool, the granule
> >> allocations have to be contiguous allocations of memory -contiguous,
that
> >> is, with what was already there.
> >>
> >> Regards
> >> HJR
> >>
> >>
> >> "sg" <s4v4g3_at_europe.com> wrote in message
> >> news:3D14FFD2.2040303_at_europe.com...
> >>
> >>>Does anyone know if no matter how we set the shared pool and db cache
> >>>Oracle's memory consumption at OS level will always equal to
> >>>sga_max_size? I set a pretty low db cache and shared pool and a large
> >>>sga_max_size and when I do show sga it actually syas that the
> >>>sga_max_size sga is allocated. Does Oracle reserve sga_max_size memory
> >>>at OS level since instance startup?
> >>>
> >>>
> >>
> >>
> >
>
> --
> Thomas Kyte (tkyte@oracle.com) http://asktom.oracle.com/
> Expert one on one Oracle, programming techniques and solutions for Oracle.
> http://www.amazon.com/exec/obidos/ASIN/1861004826/
> Opinions are mine and do not necessarily reflect those of Oracle Corp
>
Received on Sun Jun 23 2002 - 14:35:54 CDT
